Conventionally, vehicles such as electric vehicles (EV) and plug-in hybrid vehicles (PHV) are equipped with electricity storage devices such as lithium ion rechargeable batteries that store electricity to be supplied to motors. As described in, for example, Patent Document 1, such an electricity storage device has electrode assemblies, each of which has positive electrodes and negative electrodes stacked and layered while being insulated from each other.
In Patent Document 1, the negative electrodes each include a metal foil and an active material layer covering the surface of the metal foil, and the active material layer of the negative electrode contains carbon-based material as active material. Patent Document 1 specifies the density and the surface roughness of the carbon-based material to limit expansion of the active material layer of the negative electrode due to charging and discharging.